- 241 - The licensee estimates that for the JHR facility as a whole the margins with respect to the DBE are between 1.5 and 2, but does not provide any elements for assessing the plausibility of exceeding these seismic margins. Measures to improve the safety of the facility; opinion of ASN Apart from the proposals figuring in the CSA report, the CEA has undertaken, further to the CSA review, to take a number of measures to reinforce the robustness of the facilities to the seismic risk: consolidate the evaluation of the margins of the safeguard buildings (BAS) and explain the 50% margin evaluation for the nailed wall; consider the primary cooling system and the pile block as equipment essential for core cooling by the safeguard circuits or the mixing pump, and evaluate their robustness beyond the DBE accordingly; evaluate with respect to the core meltdown risk, the margins beyond the DBE with respect to the risk of neutron-absorbing rods rising under the effect of the vertical acceleration. Lastly, ASN considers that the licensee must evaluate the design margins of the cranes of the nuclear auxiliary building (BUA) beyond the DBE level, an evaluation that was not carried out in its complementary safety assessment. ASN will formulate requests on these points to the licensee, some of which will be binding requirements. Phénix Design and conformity of the facility Two seismic intensity levels of VII and VIII were taken into account in the design of the Phénix facility structures and equipment respectively. The Marcoule site seismicity studies in 1983 led to the following events being retained in application of RFS 81: the Châteauneuf earthquake (1873) with an epicentral intensity of VII-VIII brought to beneath the site; the Provence earthquake (1909) of epicentral intensity IX, magnitude 6.2 at 35 km from the site; the earthquake associated with the Nimes fault, of epicentral intensity VII, magnitude 4.9, at a distance of 10 km from the site. When the seismic behaviour of the NPP was reassessed in the 1990's to verify the safety of the facility in the event of a MHPE of intensity VII-VIII, the spectra used for the seismic re-evaluation were: a so-called "EDF" spectrum set at 0.15 g; a spectrum representing the near earthquake RFS 81 set at 0.2 g. The seismic reassessment of the facility's civil engineering structures was performed considering the envelope of the two spectra representing the reference distant earthquakes for the Marcoule site of MHPE level and one spectrum representing the near earthquake of MHPE in application of RFS I.2.of 1st October 1980. This reassessment led to the implementation of substantial reinforcements, particularly in the buildings and equipment such as the travelling cranes. With regard to building and equipment conformity, the CEA indicates in its CSA report it can guarantee their conformity thanks to permanent or periodic monitoring of certain parameters in various NPP operating configurations, routine tests of equipment items that do not function permanently, regulatory inspections and verification that the modifications have no impact on the seismic resistance of the equipment and buildings. Evaluation of the safety margins To evaluate the robustness of this facility, the CEA identified elementary margins for the structures and equipment.
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